As we all know, you have to be careful how much emphasis you place on statistics. They can be very pertinent or they can be misleading.
In the case of running backs, I tend to put yards per carry in the 'can be misleading' category.
The most important, by far, contribution of the running game is to keep drives alive. Sporadic long runs by themselves are not productive enough.
For example, as a purely imaginary hypothetical, let's imagine a drive with Maroney versus Morris or Jordan.
Maroney runs for 12 yds, 2 yds, 2 yds, and 3.6 yards. Average: 4.4 yards per carry. Results: 4 plays and out.
Jordan or Morris run for 4, 3, 3.2 - 3, 4.5, 2.6 - 2.9, 4.2, 3.2 -
Average: 3.4 yards per carry. Results: 9 plays and the drive continues.
A pretty fair amount of Maroney's 4.4 ypc come from long runs - and there are a lot that are -2, -1, 1, 1.5, 2 etc.
If the name of the game is marching down the field without punting - well ......